The medications that help thousands of children fight off cancer also have a dangerous side: They can cause life-threatening heart damage. Now City of Hope researchers have found a potential way to identify children most at risk for these effects before kids ever start treatment.

The findings, reported online Nov. 28 in the Journal of Clinical Oncology, bring scientists a step closer to genetic tests that might reduce cancer patients’ risk of cardiomyopathy, a life-threatening weakening of the heart muscle, after taking drugs called anthracyclines.

“Anthracyclines are very powerful drugs that help us fight leukemia, lymphoma and other cancers in children, as well as diseases like breast cancers in adults,” says Smita Bhatia, M.D., M.P.H., Ruth Ziegler Chair in Population Sciences and senior author on the study. About half of today’s frontline cancer regimens include these drugs.

The study involved nearly 500 teens and young adults nationwide who were treated for pediatric cancer, including 170 who later developed heart problems — the largest such study ever reported. Researchers found that patients who had a particular, common genetic factor faced a high risk of developing cardiomyopathy even after using low doses of anthracyclines.

Now that they know this genetic factor spotlights patients who are likely to develop heart problems, the scientists hope to help develop genetic tests that physicians could use to test for risk. Physicians could adjust their treatments in these children to protect their hearts. The researchers also plan to follow more patients and are conducting genome-wide studies to look for other genes that play a part.

Cardiomyopathy is one of many late effects of childhood cancer treatment, and Bhatia and her colleagues are attacking these late effects from many angles. “The science is really coming together in this area,” Bhatia says, “and it’s exciting for us to be finding answers to a significant problem.”